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Acoustic performance of composite flooring – Meeting the requirements of Part E of the Building Regulations

30 April 2013 No Comment

In the first part of our look at acoustic performance of composite flooring Mark Davies, Technical Manager, ComFlor® looks at the requirements of meeting Part E of the building regulations.

Steel construction is increasingly used in residential apartment buildings and mixed-use developments where the benefits of speed of construction, quality and off-site prefabrication are important. Steel is a quality assured, accurate, high strength, long life, adaptable, recycled and recyclable material, manufactured to tight specifications. It does not suffer from distortion or movement due to changes in moisture content. This results in easier fixing of linings and higher quality finishes, avoiding problems such as cracking around door architraves and skirtings.

Composite floors consist of profiled (galvanised) steel decking and an in-situ reinforced concrete topping. The decking not only acts as permanent formwork to the concrete, but also provides sufficient shear bond with the concrete so that, when the concrete has gained strength, the two materials act together compositely.

The main benefits of composite floors include the following:

  • Speed of construction
  • Safe method of construction
  • Saving in storage and transport
  • Structural stability
  • Easy installation

Composite floors can use deep or shallow deck profiles. There are two generic types of shallow decking are re-entrant (dovetail) and trapezoidal profiles.

Acoustic performance has increased in importance in residential buildings as developers and occupants demand higher standards. Amendments to Part E of the Building Regulations came into effect in July 2003, which introduces a new measurement index, Ctr. This takes into account of the low frequency sounds that often cause problems in residential buildings, e.g. traffic and bass music.

The new regulations set more demanding requirements for the performance of separating floors and walls between dwellings, where composite floors are a very effective way of constructing separating floors with good acoustic performance. They rely on the use of some structural mass, a suspended plasterboard ceiling and a resilient floor system on the top surface to achieve excellent acoustic performance.

The purpose of this article is therefore to highlight to the designer, the relevant information provided by the SCI publication P372, P321 and P322, and provide an introduction to the SCI/Tata Steel web based software entitled ‘Acoustic Performance Prediction Tool For Separating Floors and Walls’.

To access the tool go to: www.tatasteelapps.com/acousticperformance

Additional background acoustic information regarding principles of sound, namely airborne and impact sound, airborne and impact insulation, single figure rating values and direct and flanking transmission can be found on my other supplementary blog on acoustics, entitled ‘Acoustic Performance of Composite Floors – Acoustic Principles’.

This article is broken down into 4 main sections:

  1. Acoustic regulations – Part E of the Building Regulations
  2. Demonstrating Compliance with Part E
  3. SCI/Tata Steel web based Acoustic prediction tool
  4. Summary

1. Acoustic regulations – Part E of the Building Regulations

The acoustic requirements of residential buildings are normally given in national building regulations and associated guidance documents. For England and Wales acoustic performance requirements are given in Part E of the Building Regulations 2000and in Approved Document E. Similar equivalent documents exist for use in Scotland and Northern Ireland.

Part E of the Building Regulations

The full scope of Part E covers:

  • Acoustic insulation of separating walls and floors between newly built dwellings, and dwellings formed by a material change of use.
  • Acoustic insulation between hotel rooms, boarding house rooms, and other rooms used for residential purposes such as student halls of residence and key worker accommodation, formed by new-build or by a material change of use.
  • Acoustic insulation between rooms within a dwelling formed by new-build or by a material change of use.
  • Acoustic characteristics of common parts of apartment buildings.
  • Acoustic characteristics of schools.

Only Requirement E1 of Part E of the Building Regulations has an influence on the construction and detailing of the structural frame and floor.

Requirement E1 relates to separating walls and floors, and their junction details. The other regulations in Part E refer to surface finishes, partition walls and other building types. Requirement E1 states:

E1: Protection against sound from other parts of the building and adjoining buildings

Dwelling-houses, flats and rooms for residential purposes shall be designed and constructed in such a way that they provide reasonable resistance to sound from other parts of the same building and from adjoining buildings.

Rooms for residential purposes, as referred to in requirement E1, include rooms in hotels, hostels, boarding houses, halls of residence and residential homes etc. but do not including rooms in hospitals, or other similar establishments, used for patient accommodation.

Approved Document E provides guidance on how the Regulations may be satisfied and sets acoustic performance standards. The required levels of insulation to airborne and impact sound are summarised in Table 1 and Table 2 respectively.

Table 1. Airborne sound insulation requirements

airbourne-sound-insulation

Table 2. Impact sound insulation requirements impact-sound

2. Demonstrating Compliance with Part E

Approved Document E describes two methods of demonstrating compliance with Part E of the Building Regulations; pre-completion testing (PCT) and by use of Robust Details (RD).

PCT is carried out on-site and the onus is on the builder to demonstrate compliance. It is recommended that 1 in 10 of each type of construction detail is tested. PCT only applies to separating walls and floors and is not necessary for internal walls and floors. PCT should be carried out when the rooms either side of the separating element are essentially complete, except for decoration. Tests are generally required to be carried out without non-permanent decorative floor coverings (e.g. carpet, laminate flooring, vinyl). In some cases integral soft floor coverings are permitted, provided the floor covering is glued to the concrete slab below.

Robust Details (RD) were developed as an alternative to PCT. A range of details has been developed which have been proved through testing to consistently satisfy (and exceed) the acoustic performance requirements specified in Approved Document E. The available RD and their specification requirements are published in a handbook by Robust Details Limited. To use a Part E Robust Detail in the construction process, builders must first obtain permission from Robust Details Limited and pay the requisite fee for each dwelling. Provided that the Robust Details are built correctly, this will be accepted by building control bodies in England and Wales as evidence that the homes are exempt from PCT. Information on Robust Details can be found here.

A typical shallow composite floor system RD is presented in Section 3.1.1 of the document SCI Publication 372. Where this is the case, the RD reference is given. Some of the recommended junction details in B.2 and B.3 are also RD, provided that the wall, floor and junction are specified to comply with the requirements given in the Robust Details Handbook.

SCI Publications P321 ‘Acoustic Performance of Slimdek’ and P322 ‘Acoustic Performance of Composite Floors’ provide alternative composite floor constructions, such as screed, platform, raft and cradled floors, again to RD specification, which is further explained below. Acoustic insulation is often associated with high mass constructions. However, this is constructionally and economically inefficient, and is inappropriate for dry assembled construction. Furthermore, there is a need for resilient layers to be introduced to deal with the effect of impact sound, even in concrete floors. Composite floor constructions provide a mixture of mass and resilient layers. Multiple layers are used to provide very good levels of acoustic insulation. The mass is provided by the composite slab, and acoustic testing in buildings has shown that generally the effective mass of the slab per m2of floor area can be used to predict performance. The resilience is provided by mounting the plasterboard on a proprietary metal frame ceiling. This decouples the ceiling from the slab and reduces sound transfer. In addition, a variety of acoustic floors can be used on top of the slab to decouple the floor finish from the slab.

The alternative shallow floor finishes taken from SCI P322 are shown in Figure 1, 2, 3 and 4. There are four principal options, set out below in increasing level of likely performance. Although the similar construction details for the TATA Steel deep deck systems are not provided in this article, they are provided in SCI P321.

Screed floor

  • Sand and cement or proprietary lightweight screed.
  • Resilient layer of dense mineral wool, plastic insulant, or a polyethylene layer carefully installed to ensure continuity. The resilient layer should be turned up at the edges of the floor to isolate the walls from the screed.
  • Re-entrant or trapezoidal composite floor slab.
  • Gypsum plasterboard ceiling.

Single Figure Rating – DnT,w+Ctr = 50 to 57 dB, L’nT,w = 40 to 50 dB

Figure 1: Screed Floor
screed4

Platform floor (RSD)

  • 18 mm chipboard or similar finish layer.
  • Optional 19 mm gypsum board.
  • A resilient layer of dense mineral wool or plastic insulant. The resilient layer should be turned up at the edges of the floor to isolate the walls from the chipboard.
  • Re-entrant or trapezoidal composite floor slab.
  • Gypsum plasterboard ceiling.

Single Figure Rating – DnT,w+Ctr = 52 to 57 dB, L’nT,w = 40 to 45 dB

Figure 2. Platform Floor
platform-floor

Raft Floor

  • 18 mm chipboard or similar finish layer.
  • Optional 19 mm gypsum board for improved performance.
  • Proprietary timber batten bonded to foam strip (optional thin layer of insulation between the battens).
  • Re-entrant or trapezoidal composite floor slab.
  • Gypsum plasterboard ceiling.

Single Figure Rating – DnT,w+Ctr = 54 to 58 dB, L’nT,w = 35 to 45 dB

Figure 3. Raft Floor
raft-floor

Cradle floor (RSD)

  • 18 mm chipboard or similar finish layer.
  • Optional 19 mm gypsum board for improved performance.
  • Proprietary cradle floor supporting timber battens (with an optional thin layer of insulation between the battens).
  • Re-entrant or trapezoidal composite floor slab.
  • Gypsum plasterboard ceiling.

Single Figure Rating – DnT,w+Ctr = 54 to 58 dB, L’nT,w = 35 to 45 dB

Figure 4. Cradle Floor
cradle-floor

Note 1: The composite slab can use either a re-entrant or trapezoidal galvanized steel deck, typically 50 mm to 100 mm deep, with a concrete floor covering to give a typical overall slab depth of 130 mm to 200 mm (typically 250 to 425 kg/m2).

Note 2: The plasterboard ceiling can be fixed using a proprietary metal frame system fixed to the underside of the deck. One layer of wall board is generally sufficient, but an improvement can be achieved by using acoustic boards or 2 layers of wall board.

Note 3: The indicative performance figures are based on 45 test results from 9 buildings using composite floors.

The ceiling usually consists of one or two layers of gypsum plasterboard fixed to a metal frame system that is fixed to the underside of the steel deck. This reduces the rigidity of the connection between the plasterboard and the structure above, reducing the acoustic vibration that is transmitted.

Impact sound transmission is reduced by:

  • Specifying an appropriate resilient layer below the finish floor board with correct dynamic stiffness under imposed loadings
  • Ensuring that the resilient layer is durable.
  • Isolating the floating floor surface from the surrounding structure at the floor edges. This can be achieved by ensuring a resilient strip is included around the edges of the walking surface.

Guidance constructions, that when built correctly should provide the required acoustic performances, are provided in Approved Document E. However, these are generally conservative solutions and still require PCT to be carried out.

Both methods of compliance (PCT and RD) can be used for steel construction, although pre-completion testing is probably the most appropriate because it allows more flexibility in the design and detailing. The scope of the current range of RD for steel construction is not sufficient to include all the junction details that are typically present on a residential development. Therefore, even if RD have been used there will usually be some junctions where building control could request site testing. The range of RD is continually growing so over time more there will be fewer instances where RD cannot be used. The approval process for new RD requires significant amounts of site test data for similar details, for the tests to show that the details exceed the Building Regulation requirements by 5 dB on average and for the details to become public. Hence, there is often little incentive for system suppliers to share their information if they are satisfied with the results obtained from PCT.

3. SCI/TATA Steel web based Acoustic prediction tool

The Steel Construction Institute (SCI) has developed an on-line tool to provide structural engineers and architects with a quick and easy-to-use system for working out the likely level of acoustic performance for various forms of construction. The tool was developed with funding from Tata Steel.

The new tool is able to estimate the acoustic insulation provided by different walls and floor systems used in steel construction. The tool allows the input of different materials and combinations enabling the user to carry out a ‘what if’ analysis before embarking on a detailed design.

Composite flooring choices include The Slimdek system from Tata Steel and shallow deck composite flooring supported on steel beams. Users can also select from a range of floor treatments and ceiling options. Wall forms are based on light steel framing options including single frame or twin frames with or without acoustic quilting, and a range of different boarding options. For both walls and floors the airborne sound insulation performance is predicted.

Additionally, for floors the impact sound performance is predicted. The acoustic performance values calculated by the tool are based on the empirical interpretation of actual test data obtained from structures in the residential, health and school sectors. The input parameters of the tool are constrained within specific limits to reflect the range of the source data that has been used to develop the empirical calculation procedure.

The values predicted by this on-line tool are only intended to be used for preliminary design purposes because there are many other factors besides specification of the wall or floor format that will affect acoustic performance e.g. junction details, exact specification of products, adjoining construction form and workmanship during construction. Screens shots of a typical trapezoidal composite floor deck and twin stud wall are shown in Figures 5 and 6 respectively.

To access the tool go to:  www.tatasteelapps.com/acousticperformance.

Figure 5. Screen shot of on-line acoustic performance prediction tool for floors
acoustic-tool1

Figure 6. Screen shot of on-line acoustic performance prediction tool for walls
acoustic-tool2

4. Summary

Having highlighted the relevant details provided by the SCI publication 321, 322 and 372, this article can be summarised as follows: Composite floors can achieve excellent standards of acoustic performance.

Good acoustic insulation is achieved through a mixture of mass provided by the composite slab and an appropriately designed acoustic floor covering and suspended floor ceiling.

Acoustic raft or platform floors are preferred on separating floors to deal with impact sound transmission.

Good site practice is important to ensure that details are correctly constructed.

Sources of Information

The Steel Construction Institute
01344 636525
www.steel-sci.org

Tata Steel Construction Centre Construction Advisory Service
Tel: 01724 405060
www.tatasteelconstruction.com

Tata Steel Panels and Profiles
Tel 01244 892199
www.tatasteelconstruction.com/en/about_us/panels_profiles/

Metal Cladding and Roofing Manufacturers Association (MCRMA)
01633 895633
www.mcrma.co.uk

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